The present invention relates to methods, compounds, compositions and kits useful for delivering to a target site a targeting moiety that is conjugated to one member of a ligand/anti-ligand pair. After localization and clearance of the targeting moiety conjugate, direct or indirect binding of a diagnostic or therapeutic agent conjugate at the target site occurs. Methods for radiometal labeling of biotin or other small molecules, as well as the related compounds, are also disclosed. Clearing agents and clearance mechanisms are discussed, which agents or mechanisms facilitate a decrease in the serum half-life of targeting moiety-ligand or targeting moiety-anti-ligand conjugates.
Conventional cancer therapy is plagued by two problems. The generally attainable targeting ratio (ratio of administered dose localizing to tumor versus administered dose circulating in blood or ratio of administered dose localizing to tumor versus administered dose migrating to bone marrow) is low. Also, the absolute dose of radiation or therapeutic agent delivered to the tumor is insufficient in many cases to elicit a significant tumor response. Improvement in targeting ratio or absolute dose to tumor is sought.
The present invention is directed to diagnostic and therapeutic pretargeting methods, moieties useful therein and methods of making those moieties. Such pretargeting methods are characterized by an improved targeting ratio or increased absolute dose to the target cell sites in comparison to conventional cancer therapy.
The present invention provides clearing agents that incorporate ligand derivatives or anti-ligand derivatives, wherein such derivatives exhibit a lower affinity for the complementary ligand/anti-ligand pair member than the native form of the compound. In embodiments of the present invention employing a biotin-avidin or biotin-streptavidin ligand/anti-ligand pair, preferred clearing agents incorporate either a biotin derivative exhibiting a lower affinity for avidin or streptavidin than biotin or an avidin or a streptavidin derivative exhibiting a lower affinity for biotin than avidin or streptavidin. Preferred biotin derivatives for use in the practice of the present invention are 2xe2x80x2-thiobiotin, desthiobiotin, 1-oxy-biotin, 1-oxy-2xe2x80x2-thiobiotin, 1-sulfoxide-biotin, 1-sulfoxide-2xe2x80x2-thiobiotin, 1-sulfone-biotin, 1-sulfone-2xe2x80x2-thiobiotin, lipoic acid imminobiotin and the like.
The present invention further provides methods of increasing active agent localization at a target cell site of a mammalian recipient, which methods include:
administering to the recipient a first conjugate comprising a targeting moiety and a member of a ligand-anti-ligand binding pair;
thereafter administering to the recipient a clearing agent capable of directing the clearance of circulating first conjugate via hepatocyte receptors of the recipient, wherein the clearing agent does not incorporate a member of the ligand-anti-ligand binding pair or a lower binding affinity derivative thereof; or
thereafter administering to the recipient a clearing agent capable of directing the clearance of circulating first conjugate via hepatocyte receptors of the recipient, wherein the clearing agent incorporates a lower binding affinity derivative of a ligand/anti-ligand binding pair member, wherein the second conjugate binding pair member is complementary to that of the first conjugate; and
subsequently administering to the recipient a second conjugate comprising an active agent and a ligand/anti-ligand binding pair member, wherein the second conjugate binding pair member is complementary to that of the first conjugate.
In addition, the present invention provides methods of increasing active agent localization at a target cell site of a mammalian recipient, which methods include:
administering to the recipient a receptor blocking agent in an amount sufficient to substantially block a subpopulation of hepatocyte receptors;
administering to the recipient a first conjugate comprising a targeting moiety, a hepatocyte receptor recognizing agent, and a member of a ligand-anti-ligand binding pair; and
subsequently administering to the recipient a second conjugate comprising an active agent and a ligand/anti-ligand binding pair member, wherein the second conjugate binding pair member is complementary to that of the first conjugate.
For this embodiment of the present invention, preferred receptor blocking agents include galactose-IgG conjugate, asialorosomucoid galactosylated biotins and other small molecule clearing agents and the like. The receptor blocking agents are preferably administered in multiple doses over time to facilitate substantially continuous blockage of a substantial portion of the relevant hepatocyte receptors. The receptor becomes deblocked through receptor-based clearance of the blocking agent and cessation of administration of such blocking agent. Preferably, the cessation/clearance events occur after a time sufficient to permit localization of the targeting moiety to target sites. In addition, the second conjugate is preferably administered after a time sufficient to permit receptor-based clearance of circulating first conjugate.